1. Field of the Invention
The present invention relates to a driving circuit of a display device. Besides, the present invention relates to a display device using the driving circuit.
2. Description of the Related Art
Techniques of manufacturing a semiconductor device, for example, a thin film transistor (TFT), which has a semiconductor thin film formed on an inexpensive glass substrate, have been making rapid progress in recent years. This is because there is an increasing demand for active matrix liquid crystal display devices (hereafter referred to as liquid crystal display devices).
In the liquid crystal display device, several hundred thousands to several millions of TFTs are arranged in matrix in a pixel portion, and electric charges going into and out of pixel electrodes that are connected to each TFT are controlled by the switching function of the TFTs.
Conventionally, thin film transistors using an amorphous silicon film formed on a glass substrate are arranged in the pixel portion.
Further, in recent years, a technique is known in which quartz is utilized as a substrate and thin film transistors are manufactured using a polycrystalline silicon film. In this case, both a driver circuit and a pixel portion are integrally formed on the quartz substrate.
Still further, recently, a technique in which thin film transistors using a crystalline silicon film are formed on a glass substrate by laser annealing or the like is also known.
Liquid crystal display devices are mainly used in notebook personal computers. Different from analog data used in the current television signals (NTSC or PAL) or the like, the personal computer outputs digital data to a display device. Conventionally, digital data from a personal computer are converted into analog data and then inputted into the liquid crystal display device, or to a liquid crystal display device that utilizes an externally attached digital driver.
Therefore, a liquid crystal display device having a digital interface capable of directly inputting digital data from outside is in the spotlight.
Here, FIG. 17 shows a part of a source driver of a liquid crystal display device including a digital interface to which attention has been paid recently. In FIG. 17, reference numeral 8000 designates a shift register circuit which includes a plurality of register circuits 8010. The register circuit is constituted by four clocked inverter circuits and a NAND circuit. Reference numeral 8100 designates a sampling circuit which includes a plurality of analog switches 8110.
Note that a scan direction switching circuit is included in the shift register circuit 8000 shown in FIG. 17. The scan direction switching circuit is a circuit for controlling the order of the output of the timing pulse from the shift register circuit 8000 from left to right or from right to left in accordance with a scan direction switching signal inputted from outside.
The shift register circuit 8000 generates a timing pulse on the basis of a clock signal (CLK), a clock inversion signal (CLKB), and a start pulse supplied from the outside and sends the timing pulse to the sampling circuit. The sampling circuit 8100 samples (takes in) analog video data (VIDEO) inputted from the outside on the basis of the timing pulse from the shift register circuit 8000, and outputs to a source signal line.
In the conventional shift register circuit 8000 as shown in FIG. 17, one register circuit 8010 is constituted by four clocked inverter circuits and a NAND circuit, the shift register circuit 8000 is complicated, and the number of elements constituting it is large. Under the present circumstances in which a liquid crystal display device of higher resolution is demanded, with the improvement of the resolution, the area of the shift register circuit becomes large, and the number of elements constituting the shift register circuit is also increased.
Because of this increase in the number of elements, the production yield in the entire liquid crystal display device may become worse. Further, if the possessed surface area of the circuits becomes larger, it hinders the making of small scale liquid crystal display devices.